Electromagnetic relay having novel field pieces and a novel coil bobbin



Feb. 8, 1966 R. E. H. CARPENTER 3,

7 ELECTROMAGNETIC RELAY HAVING NOVEL FIELD PIECES AND A NOV-EL COIL BOBBIN Filed April 6, 1961 5 Sheets-Sheet 1 13 r n I2 15 45 Flg3.

3% [NI/ENE BY M $3M A TToRA/m Feb. 1956 R. E. H. CARPENTER 3,234,345

ELECTROMAGNETIC RELAY HAVING NOVEL FIELD PIECES AND A NOVEL COIL BOBBIN Filed April 6, 1961 3 Sheets-Sheet 2 A TTORNEY Feb. 8, 1966 R. E. H. CARPENTER 3,234,345

ELECTROMAGNETIC RELAY HAVING NOVEL FIELD PIECES AND A NOVEL COIL BOBBIN Filed April 6, 1961 3 Sheets-Sheet 5 r 89 69-+ Z. i 77'" I: 65 g ll 67 I i 61 I 76 @mmm- 6 5 74 72 64 73 M/VENTOR United States Patent 3,234,345 ELECTROMAGNETIC RELAY HAVING NOVEL FIELD PIECES AND A NOVEL COIL BOBBIN Rupert Evan Howard Carpenter, 35 Croham Valley Road, South Croydon, England Filed Apr. 6, 1961, Ser. No. 101,190 Claims priority, application Great Britain, Apr. 11, 1960, 12,886/60; June 21, 1960, 21,750/60 12 Claims. (Cl. 200-104) The present invention relates to electromagnetic devices such as electromagnetic relays including a magnetic circuit of the type having an energising winding and two pole pieces disposed adjacent an armature mounted so as to be capable of angular movements, the armature rocking in response to operating signals in the energising winding which embraces a core of ferromagnetic material in the magnetic circuit.

It is an object of the invention to provide an improved construction for these electromagnetic devices which enables the two primary requirements of compactness and efficiency to be met to a high degree.

This object is met by making the said pole pieces L shaped so that each has first and second limbs. The first limbs engage the two ends of the core respectively. The second limbs extend alongside the winding each from the end of the core towards the other end. Each second limb has a pole face which confronts a face of the armature across a working gap, the pole faces being flat and lying in spaced parallel planes. The axis of angular movement of the armature lies between the said planes and parallel thereto.

The said axis may be defined by pivotal bearings or by a torsion suspension for example. This construction lends itself to the production of a compact and efficient device because a relatively large armature can be accommodated alongside the winding between the said parallel planes without requiring any dirnensions of the device to be unduly long. The contact structure in the case of a relay can be mounted conveniently at the end of the winding and armature. The resulting arrangement is compact in the sense that the space within an enclosure closely surrounding the device is utilised efiiciently.

The armature can be. a polarised armature or a nonpolarised armature and in the former case the armature can be polarised by means of a permanent magnet or by means of a steady or alternating magnetic field provided by an electromagnet. If the armature be polarised, its poles should clearly be between the two pole faces where they overlap and will be spaced in a direction approximately parallel to the said planes to either side of the axis of angular movement. Throughout this specification and in the claims displacement to the side of the axis of angular movement refers to displacement in the said direction. In the ca-se'of a non-polarised armature it is necessary in order to apply a couple to the armature to have :a part thereof to one side of the axis of angular movement at least affected more by one pole piece than the other. This can be done by removing part or all of that region-of the said other pole piece which otherwise confronts the said part of the armature or by so shaping the armature that Whilst the said part of the armature lies between opposed parts of the two pole faces, the average gap between the part and the one pole face is always appreciably smaller than the average gap between the part and the other pole face.

It will usually be desirable to arrange by such means that one part of the armature to one side of the axis of angular movement is affected more by one pole piece than the other and a part of the armature to the other side of the axis is affected more by the other pole piece than the one.

Theoretically the axis of angular movement can have any direction parallel to the said planes but in practice only two are likely to be employed. In the first the axis is parallel with the length of the winding core. This has the advantage taht a spindle can extend from the armature along the axis to carry an active relay contact which cooperates with passive contacts supported at one end of the windings. The second direction is at right angles to the length of the core, that is in a plane perpendicular to the length of the core.

The pole pieces can each be of one-piece construction or built up of separate parts. For example the two limbs of each lpole piece can be separate parts.

The invention is further concerned with the problem of making a magnetic circuit of low and reproducible reluctance as is necessary, for example, in a relay required to be of high sensitivity. When a magnetic circuit is fabricated from a number of parts of magnetically soft material, however high the permeability of that material, the circuit as a whole will not have low reluctance if the junctions between the parts introduce high reluctance. The reluctance introduced at a junction depends on the air gap at that junction and the area of the junction. Appreciable reluctance is of course unavoidable at the working gaps between the armature and pole pieces. It is most desirable that the reluctance of all junctions between parts of the circuit should be smaller than the reluctance of the working gaps.

In magnetic circuits of large dimensions, such as are used in dynamo-electric machinery, it is possible, using ordinary manufacturing processes to get air gaps at junctions which are sufiiciently small in relation to the dimensions of the circuit and in relation to the overall reluctance of the circuit. Thus mating surfaces can be ground accurately and procedures such as shrink-fitting be adopted. Where small magnetic circuits, as used in relays for example, are concerned the absolute magnitude of tolerable reluctance-s is extremely small. Manufacturing tolerances are therefore extremely small and it is often impossible, solely by the adoption of ordinary manufacturing processes, to obtain the required result-s except at prohibitive expense.

To this end, in one constructional form of the invention, the winding is located on a bobbin. The bobbin comprises .a stem of magnetic material and two plate-like end cheeks which are likewise of magnetic material. The end cheeks are perpendicular to the length of the stem and low reluctance junctions are formed between the outer faces of the end cheeks and the respective pole pieces.

The low reluctance is desirably not more than a quarter that of the working gap between either pole piece and the armature. It is preferable for the reluctance of the cheek-pole piece junctions to be even smaller, say no more than a tenth that of the working gap reluctance.

These low reluctances are possible with the construction according to the invention because of the large junction area available. The junction area available is the surface area of the outer face of the cheek and it is desirable that each part of this area should be in as close proximity with the corresponding part of the pole piece as is rea-. sonably possible. The ideal would be contact over the whole surface area but in practice this will usually require prohibitively close manufacturing tolerances. Nevertheless there is no difliculty in getting a mean gap at the junction which is considerably shorter than the working gap (gap lengths being measured between the opposed surfaces defining the gap). Moreover the junction area can readily be made of the same order of magnitude as the area of the working gaps and it is not difiicultto arrive at a junction reluctance say one tenth that of each working gap.

-It will be appreciated that, even if the junction reluctance exhibits marked percentage variations on account of manufacturing tolerances, the overall circuit reluctance will not vary markedly. Consistency of circuit reluctance can therefore be maintained in production as is desirable in the case of a high sensitivity relay for example.

The stem and checks can be of integral construction or the cheeks can be fitted tightly on the ends of the stem, the cheeks being provided with bores to receive the ends of the stem. The gaps at the stem-cheek junctions present in this latter alternative can be made small relatively easily. Thus in vorder to obtain the necessary tight fit in the bore in the cheek the end of the stern may be an interference fit in the bore or be a tight press fit, the assembled parts being swaged or coined as to expand the end of the stem against the walls of the bore or close the walls of the bore against the end of the stem after the stem has been pressed in. Another way of obtaining a tight fit is to form tapered threads on the end of the stern and in the bore and to screw the end of the stern into the bore. The area available for flux to pass from the stem to the cheek can be made sufiicient simply by making the depth of the bore sufficient. It is most convenient if the bore extends right through the cheekand then what is required is to make the cheek thick enough.

The outer faces of the bobbin cheeks may be fiat. If this is so the bobbin-engaging faces of the pole shoes must be accurately oriented relative to one another if good contact is to be made over the whole of the outer faces or both cheeks without deformation of the bobbin. This may cause ditficulty and it is a further object of the invention to provide a construction avoiding this difficulty. In accordance with a preferred feature of the invention the said outer faces of the bobbin cheeks are shaped to conform to caps of spheres, the centres of which are offset from one another, the bobbin-engaging faces of the pole pieces having depressions therein for the reception of the cheeks, the radius of curvature of each such depression being substantially constantand substantially the same as that of the outer face of the cheek received therein. It is convenient, though not necessary, for the radii of curvature of the outer faces of both cheeks to be the same. These measures avoid the necessity for the bobbin-engaging faces of the pole pieces being. accurately orientatedrel'ative to one another.

If the spheres had the same centres it would be necessary for the centres of curvature of the depressions in the bobbin-engaging faces to coincide when the bobbin is gripped between these faces. This would impose a restraint on the relative positions of the pole pieces and it would be diflicult to comply with this constraint accurately enough. The restraint is removed by providing an ofiset as aforesaid. The offset is most conveniently in the direction of the axis of the bobbin.

Clearly the ideal would be exact equality of the radii of curvature of the outer face of the bobbin cheek and the depression receiving the check. This cannot be ensured with ordinary manufacturing techniques. If the face of the bobbin cheek has the smaller radius of curvature the region of contact is small. (Theoretically there is only a point of contact.) If the face of the bobbin check has the larger radius of curvature the region of contact'is appreciably greater. (Theoretically there is a circle of contact.)

It should, therefore, be arranged that any departures from the design radius lead to the face of the bobbin cheek having the larger radius of curvature. Thusthe bobbin cheek radius can be specified as r-I-Ar and the radius of the depression as r-Ar where r is the design radius and Ar is a'small tolerance.

In an alternative construction embodying the invention the outer face of one check is flat and the outer face of the other cheek conforms to the cap of a sphere, the faces l of the pole pieces engaging with the cheeks being respectively hat and provided with a depression of substantially constant radius of curvature substantially equal to that of the said sphere.

The invention also comprises a bobbin for the winding of a magnetic circuit comprising a bobbin stem and two end-cheeks, all of magnetically soft ferromagnetic material, the end-c'heeks being substantially in the form of caps of two spheres respectively, the centres of the two spheres being offset from each other and the spherical surfaces of the caps forming the outer faces of the endcheeks.

Other features and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying illustrative drawings.

In the drawings:

FIG. 1 is a side elevation of a polarised miniature relay of the invention,

FIG. 2 is a front elevation of the relay,

FIG. 3 is a plan view of the relay,

FIGS. 4 and 5 are side and end views respectively of the bobbin of the relay,

FIG. 6 is a side elevation of one L-s'haped pole piece of the relay, 7

FIG. 7 is a plan view from beneath of the same FIG. 8 is a section on the line A--A in FIG. 7,

FIGS. 9 to 11 are a front elevation, side elevation and plan respectively of the polarised armature of the relay,

FIG. 12 is a side elevation of another polarised miniature relay of the invention,

FIGS. 13 and 14 are a front elevation and plan view of the same.

Referring to FIGS. 1 and 2, the relay comprises a base 10 into which are moulded contact pins 11 by means of which connection is made to the relay winding and the relay contacts. A first pole piece in the form of an L section bracket 12 is fixed to the base 10. Thus the bracket 12, made of Mumetal, has a short limb 13 parallel to the base 10 and a long limb '14 perpendicular to the base 10. Screws (not shown) pass through the base 10 and spacers 15 between the base 10 and the limb 13 into the limb 13.

The relay has a second Mumetal pole piece in the form of L section bracket 16 having a short limb 17 parallel to, but well spaced from the limb 13 and a long limb 18 parallel to the limb 14 and extending towards the limb 13. The confronting, flat, parallel faces of the long limbs 14 and 18 form the pole faces of the relay. The bracket 16 is fixed to' the bracket 12 by means of screws 19 which pass through the limb 14 and upper and lower non-magnetic spacers 20 and 21 into the limb 18. The spacers 20 and 21 ensure that the pole faces on the limbs 14 and 18 are parallel and correctly spaced apart and may be made of a non-magnetic material having as nearly the same coefiicient of expansion as Mumetal as possible.

A bobbin 22 is gripped between the short limbs 13 and 17. To this end the holes (not shown) in the limb 14 through which pass the screws 19 are elongated. In assembly the limbs 13 and 17 are pressed together to grip the bobbin 22 whilst the screws 19 are loose, the screws being tightened whilst pressure is maintained.

The bobbin 22, as may be seen more clearly in FIGS. 4 and 5, comprises a Mumetal bobbin stem 23 and two Mumetal cheeks 24 and 25. The ends of the stem 23 are inserted in bores passing centrally through the checks. in manufacture it is arranged that the stem is a tight press fit in the bores. After the stern has been pressed into the bores small Mumetal plugs 26 are forced into' blind holes bored in the ends of the stem. (The Mumetal must of course be annealed after Working in order to restore its high permeability.)

These measures ensure that the junctions between the stem and cheeks are of low reluctance. It can readily be seen that each junction will be of an area at least equal to the cross-sectional area of the stem 23 so long as thecheeks 24 and 25 have a thickness at their centres at least equal to half the radius of the stem.

The outer face of each cheek is rounded off to conform to the cap of a sphere. Radius lines 27 and 28 appropriate to the cheeks 24 and 25 respectively are shown in FIG. 4. Whilst the two spheres are of the same radius R, the bobbin is of overall length less than 2R. Thus the centres of the two spheres are offset from one another along the stem 23 as is apparent in FIG. 4.

The cheeks 24 and 25 are received in spherical depressions in the limbs 17 and 13 of the same radius R. A depression 29 of radius R in the limb 17 can be seen in the views of the bracket 16 in FIGS. 6 to 8. These figures also showthreaded holes 30 in the limb 18 for the reception of the screws 19.

his diflicult and expensive in manufacture to ensure thatthe limbs 17 and 18 and the limbs 13 and 14 form perfect right-angles with one another. Similarly, it is difficult'to make the line of the bend in each bracket 12 or 16 perfectly perpendicular to the length of the limbs of the bracket. For" these reasons the limbs 13 and 17 are unlikelyto lie accurately in parallel planes in the assembled relay. However, any such departures from pa rallelismare readily accommodated, without any widening -ofgaps or straining of the bobbin, by virtue of the arrangement'of spherical mating surfaces adopted.

It is also difficult and expensive to ensure that the centres of the depressions in the limbs 13 and 17 are accurately disposed on the intended axis of the bobbin. This would give rise to difliculty if the centres of the spheres appropriate to'the cheeks 24-and 25 were coincident. Thedifficulty is avoided by the offset between the centres and the bobbin can-assume-a position with its axis at a small angle to the intended axis (parallel to the pole faces of the limbs 14 and 18) sufiicient to take care of any lack of true positioning of the centres of the depressions.

'Before winding wire on to the bobbin a strip of insulating material is Wrapped round the stem 23 and a pair of insulating split washers are placed over the shank against the innerface of each cheek 24 and 25. A terminal tag is stuck between each pair of washers and the winding wire terminates on these tags. The tags are shown at 31 in FIG. 1, asare leads 32 extending from the tags to two of the pins 11.

The most efiicient turns of the winding on a bobbin are the turns of smallest diameter. Thus, for a given number of turns the efficiency of the winding in providing flux in the magnetic circuit is reduced if the means diameter of the turns is increased. The strip of insulating material Woundrou'nd the bobbin stem increases the said mean diameter slightly above that which would obtain if the winding was wound directly on to the stem. Even this slight increase has a measurable effect on the eificiency of the winding. A smaller increase of mean diameter can be obtained if the bobbin stem is insulated by enamelling. The insulating compound used for enamelling is preferably non-carbonaceous. A still smaller mean diameter can be obtained using anodised aluminium wire for the winding. a

The armature of the relay lies between the two pole f aces previously referred to and pivots about an axis extending'celitrally through the space between the pole faces in a direction substantially parallel to the bobbin axis and accurately parallel to the pole faces.

"The armature is shown in FIGS. 9 to 11 and comprises alce ntral permanent magnet 33 flanked by soft ironfpole pieces 34 and 35. The magnet is magnetise-d across its width, rendering the pole pieces 34 and 35 northand south poles respectively. The magnet and pole pieces are bonded together using an epoxy resin for example or are sweated together with solder. End plates 36are fixed to the armature by screws 37 and shafts 38 and 39 extend upwardly and downwardly respectively from the plates 36. The shaft 39 passes freely through the spacer 21 and terminates in a pivot 40 journalled in 6 a bearing fixed in the limb 13 of the. bracket 12. The shaft 38 has a pivot 41 journalled in a bearing fixed in the spacer 20. A rod 42 forms a prolongation of the pivot 41 and supports the active contact of the relay.

The pivot bearings are not described or shown in de' tail as they are generally as described in the specification of my Patent No. 2,891,200. Reference may be made to this specification for further details and an explanation of how the bearings are adjusted and of the advantages to be obtained with such bearings. Briefly, however, the pivots and 41 are sleeved in pieces of resilient tub i-ng 43 which fit in their turn into flanged metal sleeves 44 (FIG. 1). The metal sleeves pass freely through over-size holes in the limb 13 and spacer 20 but the flanges on the sleeves 44 seat against these members. Plates 45 and screws 46 enable the flanges to be clamped against the limb 13 and spacer 20 when the pivot bearings have been accurately positioned.

The contact assembly of the relay comprises an active (moving) contact tongue 47 fixed to the rod 42. Thus the contact tongue 47 has a threaded portion 48 bored transversely to receive the rod 42. A nut 49 on the portion 48 clamps against a fiat 50 (FIG. 10) on the rod 42,. also retaining in place a washer-like terminal tag 51. A lead 52 extends from this tag to one of the pins 11, being held in position against the limb 14 by clips 53 retained by the screws 19. It will be seen that the lead 52 is attached to the armature near the axis thereof and runs for most of its length parallel to and close to the armature axis. In this way it can be arranged that the lead exerts no appreciable force on the armature.

The passive contacts of the relay are mounted on a block 54 fixed to the limb 17 of the bracket 16. Plates 55 and 56 are fixed either side of the block 54 by screws 57 and bear contact screws 58 and 59, mica spac ers (not shown) being used to insulate the plates from the block. When the armature pivots in the clockwise direction as viewed in FIG. 3 the contact tongue 47. bears against the end of the screw 59. Pivoting in the other direction brings the contact tongue 47 against the screws 58 (as it is shown in the figure). Leads 60 extend from the plates 55 and 56 under the clips 53 to two of the pins 11. Whilst different in construction from known polarised relays as described in the specification of my Patent No. 2,816,976, the relay described does not differ in principle of operation which is therefore not described.

In an alternative way of making the bobbin 22 the outer faces of the cheeks 24 and 25 are initially made to conform only approximately to the required shape. Final shaping of each cheek is effected in a coining or diestamping operation after the checks have been fitted on the stem 23. In this same operation the end of the stem fitted into the check is expanded into the bore in the cheek and the walls of the bore close against the stem to give a low reluctance junction between the stem and the cheek.

As indicated previously the stem and cheeks may be integral with one another. One way of making a bobbin of such integral construction is to make use of the procedures of powder metallurgy, moulding, and com pacting metallic particles to the shape of the bobbin.

In the relay described the two pole pieces are both of integral construction. This is not necessary and the pole pieces can be assembled from a number of separate parts. The limbs 13, 14, 17 and 18 can be separate parts for example, and such a construction will now be described.

The relay shown in FIGS. 12 to 14 has been designed with a view to cheapness of manufacture as well as compactness and efficiency.

The winding 61 is wound on a flat H-shaped stamping instead of a bobbin, the stamping having a cross-piece 62 and top and bottom end pieces 63 and 64 (the uprights of the H). Washers 65 of insulating material form flanges confining the winding which is wound on the cross-piece 62.

A first L-shap'ed pole piece is fixed to the end piece 63 and comprises separate 'short and long limbs 66 and 67. The short 'limb is clamped against the end piece 63 by screws 6'8 whilst the long limb is clamped to the short limb by screws 69. These screws also pass through the long limb 70 of a second L-shaped pole piece and a nonmagnetic spacer 71 clamped between the limbs 67 and 79. The second pole piece has a short limb 72 fixed to the end piece 64 by screws 73 and to the limb 70 by screws 74. A second spacer 75 is held between the limbs 67 and 70.by screws 76.

A polarised armature 77, which may be constructed and mounted in the same manner as that shown in FIGS. 9, and 1'1 is pivoted between the spacers 71 and 75. An extension '78 of the upper armature pivot spindle has a contact arm 79 clamped to it by means of a block 80 and screws 81 (FIG. 14). This arm carries active contacts 82 'which co-operate with passive contacts 83. The passive contacts are mounted in metal plates 84 fixed to two .lugs 85 upstanding from the end piece 63. Thus insulating spacers 86 areplaced between the lugs 85 and plates 84 and screws 87 pass through lugs and spacers into the plates 84.

Terminal tags 88 for "the passive contacts are held under the heads of the screws .87. The tags and screws are insulated from the lugs 85 by means of insulating bushings and washers. A tag (not shown) for connection to the active contact can be held under the head of the screw 91.

The insulating spacers 86 are bridged by a platform 89 on which a spring 90 is mounted by means of a screw 91. This spring is used in known manner to increase the sensitivity of the armature and connection to the active contacts is also made by way of it.

It will be noted that all metal to metal junction in the magnetic circuit .are of the cross-sectional area of the limbs 66 and 72 which are made thick enough to obtain the desired low reluctance of the joints.

The manner of operation of the relay will be obvious to those skilled in the art.

It will also be understood that many modifications could be made in the described illustrative constructions without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An electromagnetic device, comprising a core of ferromagnetic material having first and second ends, an energising winding embracing the core, first and second pole pieces, each of which has a core-engaging limb and a gap-forming limb at substantially right angles to each other, the core-engaging limbs of the first and second pole pieces engaging the first and second ends respectively of said core at low reluctance junctions, the two-gap forming limbs being oppositely directed from the first and second core-engaging limbs towards the second and first ends respectively of the core, the gap-forming limbs having flat overlapping pole faces which lie in spaced parallel planes,a polarized armature, and means mounting said armature between said planes for angular movement about an axis parallel to and between said planes, the armature having a permanent polarizing magnet through which the said axis passes and two magnetically soft armature pole pieces flanking the said magnet and rendered north and south poles respectively thereby, the armature pole pieces being within the region of overlap of the gap-forming limbs and the armature as a whole @being of fiat form.

2. An electromagnetic device according to claim 1, comprising non-magnetic spacers between said fiat pole faces.

3. An electromagnetic device according to claim 2, wherein the said means mounting said armature comprise pivotal bearings mounted said spacers.

8, 4. An electromagnetic device comprising a bobbin of ferromagnetic material having a stem of ferromagnetic material and two end cheeks of ferromagnetic material, said end cheeks being plate-like and substantially perpendicular to said stem, an en'ergising winding embracing the stem, first and second pole pieces, each of which is L-shaped and has a cheek-engaging limb and a gap,- forming limb, the cheek-engaging limbs of the first and second pole pieces engaging the two bobbin cheeks .respectiv'ely at low reluctance junctions, the two-gap forming limbs being oppositely directed from the two cheekengaging limbs towards the respective other cheek engaging limbs, the gap-forming limbs having flat pole faces which lie in spaced parallel planes, an armature, and means mounting said armature between said planes for angular movement about an axis parallel to and between said planes, the armature having two faces which confront the said pole faces across working. gap r 5. An electromagnetic device according 'to cla i m -4 wherein the outer surfaces of the said end checks are shaped to conform to the caps of two spheres,t he cheek engaging limbs having depressions therein receiving the end cheeks, the radius of curyature of each depression being substantially constant and substantially the same as that of the outer surface of 'thecheekreceived therein.

6. An electromagnetic w device comprising a flat H-shaped core of ferromagnetic material having a cross piece joining two end pieces, an en'ergisin g winding em bracing the cross piece, first and second pole pieces, each of which is L-shaped and has a core-engaging limb and a gap-forming limb, the ends of the core-engaging limbs of the first and second pole pieces remote from the gapforming limbs being butted againstfiat facesof the said end pieces respectively at low reluctance junctions, the two-gap forming limbs being oppositely directed from the first and second core-engaging limbs towards the respective other core-engaging limbs, the gap-forming limbs having flat pole faces which lie in spaced parallel planes,- and a polarized armature mounted between said planes for angular movement about an axis parallel to and be tween said planes, the armature having a permanent .polar izing magnet through which the axis passes and two ma -j netically soft armature pole piecesfianking the said magQ net and rendered north and south poles respectively thereby, at least a major part of the armature pole pieces being within the region of overlap of the gap-forming limbs and the armature as a whole being of fiat form.

7. An electromagnetic relay comprising a core of ferromagnetic material having first and second ends, an .ener gising winding embracing the core, first and second pole pieces, each of which is L-shaped and has a core-engaging limb and a gap-forming limb, the core-engaging limbs of the first and second pole pieces engaging the fir-stand second ends respectively of said core at low reluctance junctions, the two-gap forming limbs being oppositely directed from the first and second core-engaging limbs towards the second and first ends respectively of the core, the gap-forming limbs having flat pole faces which lie in spaced parallel planes, a flat, polarized armature, means mounting said armature between said planes for angular movement about an axis parallel to and between said planes, the armature having two faces which confront the said pole faces across working gaps, passive cont-acts mounted to the side of one core-engaging limb remote from said core and an active con-tact carried by said armature for cooperation with said passive contacts.

8. A relay according to claim 7, wherein said means mounting said armature comprise two pivotal bearings, at least one of which includes a spindle fixed to thearmature and extending along said axis, said spindle having an extension and means fixing said active contact to said extension. p

9. An electromagnetic device comprising a bobbin haying a stem of ferromagnetic material and two end cheeks of ferromagnetic material, said end cheeks being plate like and substantially perpendicular to said stem, an energising winding embracing said stem, first and second pole pieces forming 10w reluctance junctions with the outer faces of said end cheeks, at least one of said end cheeks having an outer surface configuration which is a cap of a sphere and its respective pole piece having a complementary depression receiving said end cheek, whereby the pole pieces and the bobbin may be assembled with the pole pieces in relative orientations which are fixed independently of their attachment to the bobbin without causing strain at the joints between said end cheeks and said pole pieces, and an armature completing a magnetic circuit with said bobbin and pole pieces across working gaps between said armature and pole pieces.

10. An electromagnetic device according to claim 9, wherein the said outer faces of both bobbin cheeks are shaped to conform to caps of two spheres, the centres of which are offset from one another, the faces of the pole pieces which engage the end-cheeks having depressions therein receiving the cheeks, the radius of curvature of each depression being substantially constant and substantially the same as that of the outer face of the cheek received therein.

11. ,An electromagnetic device according to claim 9, wherein the outer face of one cheek is flat and the outer face of the other cheek conforms to the cap of a sphere, one pole piece having a flat face in contact with the fiat face of the one cheek and the other pole piece being provided with a depression for the reception of the said other 10 cheek and of substantially constant radius of curvature substantially equal to that of the said sphere.

12. An electromagnetic device according to claim 1, wherein the axis of angular movement of the armature is substantially parallel to the length of the core of the device.

References Cited by the Examiner UNITED STATES PATENTS 1,016,567 2/1912 Kaisling 200-104 1,104,077 7/1914 Smith 200-87 1,177,988 4/1916 Buhl 200-93 1,538,950 5/1925 Price 200-87 2,455,049 11/1948 Edwards et a1. 200-87 2,499,315 2/1950 Johnson -37 2,569,036 9/1951 Benner et a1 336-233 2,612,544 9/1952 Fisher 317-172 2,664,478 12/1953 Johansson 200-87 2,760,026 8/1956 Horlacher 200-87 2,761,929 9/1956 McLellan et a1. 317-198 2,786,187 3/1957 Nims 336- 2,810,037 10/1957 Faus et al 200-87 2,820,122 l/l958 Teszner 200-147 2,891,200 6/1959 Carpenter 317-198 2,923,794 2/1960 Keeran 200-87 BERNARD A. GILHEANY, Primary Examiner.

RICHARD M. WOOD, ROBERT K. SCHAEFFER,

Examiners. 

1. AN ELECTROMAGNETIC DEVICE, COMPRISING A CORE OF FERROMAGNETIC MATERIAL HAVING FIRST AND SECOND ENDS, AN ENERGISING WINDING EMBRACING THE CORE, FIRST AND SECOND POLE PIECES, EACH OF WHICH HAS A CORE-ENGAGING LIMB AND A GAP-FORMING LIMB AT SUBSTANTIALLY RIGHT ANGLES TO EACH OTHER, THE CORE-ENGAGING LIMBS OF THE FIRST AND SECOND POLE PIECES ENGAGING THE FIRST AND SECOND ENDS RESPECTIVELY OF SAID CORE AT LOW RELUCTANCE JUNCTIONS, THE TWO-GAP FORMING LIMBS BEING OPPOSITELY DIRECTED FROM THE FIRST AND SECOND CORE-ENGAGING LIMBS TOWARDS THE SECOND AND FIRST ENDS RESPECTIVELY OF THE CORE, THE GAP-FORMING LIMBS HAVING FLAT OVERLAPPING POLE FACES WHICH LIE IN SPACED PARALLEL PLANES, A POLARIZED ARMATURE, AND MEANS MOUNTING SAID ARMATURE BETWEEN SAID PLANES FOR ANGULAR MOVEMENT ABOUT AN AXIS PARALLEL TO AND BETWEEN SAID PLANES, THE ARMATURE HAVING A PERMANENT POLARIZING MAGNET THROUGH WHICH THE SAID AXIS PASSES AND TWO MAGNETICALLY SOFT ARMATURE POLE PIECES FLANKING THE SAID MAGNET AND RENDERED NORTH AND SOUTH POLES RESPECTIVELY THREBY, THE ARMATURE POLE PIECES BEING WITHIN THE REGION OF OVERLAP OF THE GAP-FORMING LIMBS AND THE ARMATURE AS A WHOLE BEING OF FLAT FORM. 